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Shades of Gray

Interpretation of Perioperative Imaging Installment II: Abdominal X-Rays

© 2009 Michael Sheehan, MSN, RNFA, NPc


This is Installment II of a series on perioperative imaging. Installment I is available at this link.


As Advanced Practice Nurses (APNs), we often order and rely on perioperative imaging to guide our decision making and plan our operative interventions. However, almost no BSN, RNFA, or even MSN curricula include interpretation of medical imaging. This forces us to abdicate our autonomy and rely on either the interpreting physician's "read" or our supervising physician's opinion. Learning to interpret medical imaging studies can increase our confidence and autonomy as well as increase our marketability and professional stature.


X-rays are electromagnetic radiation similar in properties to light, with shorter wavelengths than ultraviolet (UV) light. "X-rays are generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate electrons released by a hot cathode to a high velocity. The high velocity electrons collide with a metal target...creating X-rays."5 The resulting X-rays are aimed at a target and projected onto a phosporous screen and then developed in numerous ways, previously on film though most facilities are transitioning to webbased systems. The "film" is darkened by exposure to photons. The target (patient in our instance) affects the photon "throughput" and results in various shades of white, gray, and black. Denser materials will show up white and less dense materials will be shades of gray or black. It is also important to note that light energy, including X-rays, expands as it travels. This means objects closer to the X-ray tube will be smaller while those that are farther away will be enlarged. "There are only five categories of opacity visible on a radiograph, though there are varying levels of opacity within the primary categories. These categories are mineral (calcium and phosphorous as seen in bone), soft tissue and fluid (as they have the same radiographic opacity), fat, gas [the most radiolucent opacity on Xray], and metal [the most radiopaque images on X-ray]."4

How to Approach an X-Ray Image

When approaching an X-ray film, or any imaging modality, it is important to proceed systematically. This requires a firm knowledge of anatomy and physiology and the ability to translate that knowledge into three- and four- dimensional thought. You should cross-check the name, medical record number, and date on the radiograph to your patient and current date. Next, check the position of the patient in relation to the film. The radiograph should be labeled with orientation markers of left/right or anterior/posterior. Orientation plays an important role in how you will mentally evaluate the two-dimensional "shadowgram" in three dimensions. As you begin your radiographic evaluation, it is important to NOT go in with preconceptions of what you will see or "tunnel vision" that will keep you from evaluating the full exam after visualizing the "expected abnormality." Stokell (n.d.)4 noted that each shadow must be evaluated for four things: · Is it a feature of normal anatomy? · Is it a composite structure formed by the superimposition of structures? · Is it an artifact produced by poor positioning? · Is it a pathologic lesion? We are not training to become radiologists so it is not necessary, nor is it conceivable, to know all of the intricacies of radiographic interpretation. There are; however, some standard guidelines to help you get the basics down. First, is everything there that should be there? Secondly, is there anything there that shouldn't © 2009 Michael Sheehan, MSN, RNFA, NPc


be there? Third, is everything there consistent with normal? Symmetry is congruent with health in terms of evolutionary biology. If you see anything on your radiograph that is not symmetrical, you should consider it abnormal. Let's examine a "normal" radiograph of the kidneys, ureter, and bladder (KUB) below to get some practice. A KUB or abdominal plain film is often the first imaging test ordered for abdominal complaints. Though newer technologies have improved diagnostics, you should still be familiar with normal and some common abnormal KUB findings.

Example ­ Normal

Look at Fig. 1, left. First, is this your patient? Second, how old is your patient? You should try to use the "patient's age to your advantage by making sensible suggestions [i.e., a] 20-year old is much less likely to have malignancy than someone who is 70."2 I have removed the identifying information from this radiograph so we will assume that this is our 32-year old patient. Is the radiograph marked/ oriented appropriately? As we learned with CXRs, orientation is important. More than 90% of abdominal radiographs are taken in the supine position; however, some films are taken erect and fewer in the lateral decubitus position. Is the abdominal X-ray (AXR) penetrated adequately? A normal KUB should be penetrated well enough to see the lumbar vertebrae and spinous processes. Next, begin to identify the solid organs of the abdomen on the AXR. The liver can be seen in the RUQ (right upper quadrant) at the level of the 11th and 12th ribs. Using knowledge of anatomy, we know that the gallbladder is located in the RUQ. Look for calcifications in all solid organs of the abdomen, Figure 1 gallstones in the gallbladder, kidney stones in kidneys, or pleboliths (or calcified pelvic 102/images.htm veins) in the pelvis. The kidneys may or may not be visible on a correctly penetrated KUB and should be located at the level of the lowest costovertebral angle. Figure 1 shows the outline of the kidneys with long dark arrows. As you can see, the right kidney is often higher than the left. The bladder should be deep within the pelvis and is demonstrated in Fig. 1 with short dark arrows. Next, examine the musculoskeletal structures of the AXR. You should be able to see the 10th, 11th, and 12th ribs on an appropriately positioned AXR. As you can see in Fig. 1, the lumbar spine is straight without curvature or abnormalities. The sacrum is located in the middle of the AXR and flanked by the iliac crests bilaterally. Our example shows the sacroiliac joints clearly. The pubic symphisis is the dark line located at 6 o'clock at the bottom of the AXR. The femoral heads are smooth and round and the femoral neck on the right (the left is not visualized clearly) is clearly visible and free of deformities. The "A" lines from the vertebral bodies extending into the pelvis outlined by short empty arrows are the psoas muscles. As a general rule of

© 2009 Michael Sheehan, MSN, RNFA, NPc


thumb, you should be able to see these on a normal KUB. If they are not visible, there is likely an overlying abnormal finding in the bowel. As you continue to look more deeply into the radiograph, follow the guidelines above. Is the radiograph consistent with "normal"? Examine the bowel and bowel gas patterns. Fig. 1 shows a normal AXR and therefore the bowel and bowel gas patterns are difficult to appreciate. As a general rule of thumb, intraluminal gas throughout the bowel is normal. Extraluminal gas is always abnormal. The small intestine and small bowel gas patterns are considered normal if the diameter is no more than 35mm, and the large bowel patterns should be less than 55mm. We will not measure the bowel; instead we will subjectively "measure" normal. In order to get a "feel" for bowel gas and patterns, let's examine abnormal findings below.

Examples - Abnormal

Look at Fig. 2, left. First, is this your patient? How old is your patient? This is a 57-year-old female presenting with bloating, abdominal pain, and vomiting. The AXR is adequately penetrated and you can see the 10th, 11th, and 12th ribs, the thoracolumbar vertebral bodies, the sacrum, sacroiliac joints, and iliac crests. There are degenerative changes in the right SI and right hip joint (compare the two sides and look at the compressed and arthritic spaces on the right). The liver is well visualized in the RUQ; however, the kidneys are not seen due to overlying dilated bowel and gas patterns. The outline of the bladder can be seen below the lowest loop of bowel. The stomach is distended and filled with air in the epigastrum and LUQ. Obviously the bowel is dilated but in order to read the AXR adequately, we must distinguish large from small bowel. Small bowel contains lines that run the entire width of the bowel called valvulae conniventes. The large bowel will demonstrate lines called haustra that only traverse a third of the width of the bowel. The dilated loops of bowel in Fig. 2 demonstrate small bowel dilatation as evidenced by the valvulae conniventes. The next step for this patient would be to get an upright AXR to assess for air/fluid levels. In this instance, the excessive small bowel air in the absence of large bowel air is indicative of a mechanical small

Figure 2

bowel obstruction.

© 2009 Michael Sheehan, MSN, RNFA, NPc


Figs. 3 & 4

Figs. 3 and 4, above, are two X-rays of another patient. This is actually an IV pyelogram; however, we will cover it under the AXR in order to gain a better understanding of the kidneys and ureters. This is a 53-yearold male with acute flank pain and hematuria. This radiograph is adequately penetrated, allowing visualization of the distal ribs, thoracolumbar spine, proximal sacrum, bilateral SI joints, and bilateral iliac crests. The patient demonstrates a prosthetic hip with femoral and acetabular components on the right. The pelvic portion of this AXR is obscured by a lead shield to protect the patient's gonads. The liver can be seen in the RUQ. The psoas muscles forming the "A" line are appreciated. There are normal small bowel loops in the pelvis and normal air/stool seen in the ascending colon along the right border of the AXR. Again, this is a "guesstimation" of the size of the visualized bowel segments since we are not using a PACs workstation and cannot measure the bowel accurately. The kidneys are clearly visible in Fig. 3, with bowel loops superimposed over the right lower pole of the kidney. There is a small calcification seen adjacent to L2 and the left psoas muscle (presumed to be in the ureter leading from the left kidney above it). Figure 4 demonstrates adequate ureteral drainage of contrast dye, noticeable along the lateral border of the right lumbar spine and extending from the kidney towards the bladder. The left kidney does not show any drainage of dye into the ureter and shows signs of dye "congestion" throughout the kidney. The calcification is still seen at the same level. "The typical finding on IVP of acute obstruction is delayed appearance of contrast in the affected kidney, with intensification of the nephrogram on the affected side with time. This is called the obstructive nephrogram."3 This patient has acute left ureteral obstruction; in this case due to nephrolithiasis. Other causes of acute obstruction can include blood clots, infection, or surgical trauma. Acute obstruction is often localized to "the ureteropelvic junction, the pelvic brim at the crossing of the ureter and the iliac blood vessels, and the ureterovesicle junction."

© 2009 Michael Sheehan, MSN, RNFA, NPc


Figs. 5 & 6

Fig. 5 and 6, above, are from a 62-year-old man who presented with an acutely distended abdomen and appeared septic. The PA CXR demonstrates poor penetration and slight rotation evidenced by mal-rotation of the clavicles. The visualized portion of the trachea is midline and the heart is not enlarged. Notice the pronounced vascular markings in the right lung and the very clear outlines of the right and left pulmonary arteries in the hila indicating vascular congestion. The hemidiaphragms are elevated bilaterally, left greater than the right. Importantly on this upright film is the large amount of free air under the hemidiaphragms. The subsequent AXR demonstrates adequate penetration and multiple dilated loops of small and large bowel. Please note the prominent dilated segment of small bowel (evidenced by the valvulae conniventes) in the center of the AXR and compare it to Fig. 2. This is a classic example of the "double wall" sign. The means you can see the mucosal and serosal wall of the bowel indicating air on both sides of the bowel wall, intra- and extraluminal. This 62-year-old man probably had a large bowel obstruction that progressed to perforation, leading to the diagnosis of pneumoperitoneum.

© 2009 Michael Sheehan, MSN, RNFA, NPc


Figs. 7 & 8

Fig. 7 is an AXR of a 50-year-old woman presenting with intermittent RUQ pain (Fig. 8 highlights the calcified findings). As you can see, the AXR is adequately penetrated and shows no mal-rotation; however, the position is suboptimal at the caudal extent. The 10th, 11th, and 12th ribs are visualized well. The thoracolumbar spine is well visualized, straight, and without deformities. The right and left visualized iliac crests, SI joints, and acetabulums are without deformities. The liver is difficult to visualize in the RUQ; however, there are multiple rounded radiodensities seen at the level of the liver. The pancreas is visualized in the LUQ with diffusely scattered calcifications. The right kidney is not well visualized due to overlying bowel and gas. The left kidney is well visualized with a smoothly rounded calcification within the renal pelvis (the collection system of the kidney preceding the calyxes and ureters). There are multiple linear metal densities seen within the left pelvis. Finally, there is a large rounded calcification within the pelvis and anterior to the bladder. The calcifications seen in the RUQ have a more angular appearance that is characteristic of gallstones; they rub together and become faceted in the gallbladder. The diffusely scattered calcifications in the spleen could be chronic pancreatitis in a patient with a long history of alcohol abuse or could represent histoplamosis. The round opacification within the left kidney represents a renal calculus, verses a ureteral stone seen in figures 3 and 4. The metal densities seen within the left pelvis are probably surgical clips, presumably for a sterilization procedure. The large calcified mass deep in the pelvis and anterior to the bladder is consistent with a uterine fibroid. In this case, the intermittent RUQ pain is secondary to cholelithiasis with incidental findings of histoplasmosis, renal calculus, and a uterine fibroid.

© 2009 Michael Sheehan, MSN, RNFA, NPc

8 In Fig. 9, "A 35-year-old man was carjacked and forced to ride along with his assailants. He was beaten, shot twice then thrown out of the moving vehicle on to the highway. He was brought to hospital with a gunshot wound to the abdomen and to the leg. His condition was critical. A supine abdominal X-ray was done in the resuscitation bay."1 This AXR shows poor penetration and rotation of the patient to the left. There are normal bowel gas patterns seen on this AXR. As mentioned, there is a paperclip marker placed on the abdomen at the site of entry. There is a metallic foreign body (bullet) in the right lower quadrant. The author explains that "[it] is typical of a bullet to "point" to the entrance wound, provided it has not been deflected or deformed. This happens because the bullet's centre of gravity is towards its base, and it may tumble base-first as soon as it loses its gyroscopic stability which it gained from the rifling of the barrel."1 In this case, the bullet passed through the aorta and the patient did not survive despite attempts to resuscitate him.

Figure 9 %20Articles/042002/Abdomen.jpg

Abdominal X-rays are most effective in terms of diagnostic yield in the acute abdomen. The AXR is one of the first imaging studies ordered for abdominal complaints. Due to their low diagnostic yield, AXRs are often followed by ultrasounds, CT or MR, or any number of specialized procedures such as barium enemas, upper or lower GI series, or an IVP. They do provide some of the more "entertaining" findings as seen in Figures 10-13 below:

Figure 10 /2009/01/abdominal-foreignbodies1.jpg

Figure 11 quizzes/thermo.jpg

© 2009 Michael Sheehan, MSN, RNFA, NPc


Figure 13 / theweekpix2/cow158lg.jpg&imgrefurl=http://w 520158Bezoar/bezoarcorrect.htm&usg=__RDB _DYxPIcuv2NermMNVW_Iw=&h=800&w=10 7&sz=109&hl=en&start=6&um=1&tbnid=qb9x WE_gq46iM:&tbnh=112&tbnw=150&prev=/im ages%3Fq%3Dhair%2Bball%2Babdominal%2B foreign%2Bbodies%26hl%3Den%26rlz%3D1G 1GGLQ_ENUS254%26um%3D1

Figure 12 argaret/742-4619-1021410.jpg

Fig. 10 Demonstrates multiple household items in a patient with pica Fig. 11 Demonstrates an aerosol can introduced via rectum Fig. 12 Demonstrates an adult female presenting with abdominal pain, who swallowed something 6 weeks prior Fig. 13 Demonstrates a large bezoar or "hair ball" in a patient with trichotillomania

Information for the Patient

Patients often suffer anxiety regarding any medical procedure. As the APRN, we can reduce stress by providing current information regarding any diagnostic imaging. Here are some points to make for your patients' education: · An abdominal X-ray exposes the patient to >30x the amount of radiation as a chest X-ray and has significantly lower diagnostic yield; therefore, alternative imaging processes such as abdominal CTs are often preferred. · An abdominal X-ray is most useful in the patient with an acute abdomen. · Imaging with X-rays involves exposing a part of the body to a small dose of radiation · Once you are positioned, you may be asked to hold still for a few moments and you may or may not be asked to hold your breath for parts of the procedure · Women should always tell their technician or radiologist if they are pregnant or think they may be pregnant · The procedure itself should take no longer than 1 minute · Women should tell their technician if they have an IUD inserted · Patients should also mention if they have had a barium study or OTC medications such as Pepto Bristol as these may interfere with the exam © 2009 Michael Sheehan, MSN, RNFA, NPc


Review Quiz

A number of structures are identified by one- or two-letter abbreviations in the two photos below. Underneath the photos is a list of those abbreviations. Identify each one. (See answers on page 12.)

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.


© 2009 Michael Sheehan, MSN, RNFA, NPc


References 1. Bertoli, B. (1999). Firearms ID. Retrieved May 7, 2009 from s/042002/Abdomen.jpg&imgrefurl= 002/JohannesburgTraumaUnit2.htm&usg=__a5_RhZ41UExzZ6sLRnwmhQtxkU8=&h=364 &w=274&sz=9&hl=en&start=7&um=1&tbnid=udWsfF3scww6SM:&tbnh=121&tbnw=91&pr ev=/images%3Fq%3Dgunshot%2Bwound%2Babdominal%2Bx%2Bray%26hl%3Den%26rlz %3D1G1GGLQ_ENUS254%26sa%3DN%26um%3D1 2. Dick, Elizabeth (2000). Chest x-rays made easy. Retrieved April 1, 2009, from 3. Shah, K., Lamki, N. (n.d.). Radiology teaching files. Retrieved May 7, 2009, from 4. Stokell, E. (n.d.). Radiological interpretation. Retrieved April 5, 2009, from 5. (n.a.) (n.d.). X-ray. Retrieved March 31, 2009 from

© 2009 Michael Sheehan, MSN, RNFA, NPc


Answers to Review Quiz

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. AC. CE. DC. HF. L. LD. LK. LP. PF. RD. RK. RP. S. SC. SF. ST. TC. Ascending colon Cecum Descending colon Hepatic flexure Liver Left hemidiaphragm Left kidney Left psoas Properitoneal fat Right hemidiaphragm Right kidney Right psoas Spleen Sigmoid colon Splenic flexure Stomach Transverse colon

© 2009 Michael Sheehan, MSN, RNFA, NPc


January 3, 2001

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